In recent years, in the medical and graphic arts fields, a decrease in the processing effluent has been increasingly demanded from the viewpoint of environmental protection as well as space saving.
As a result, techniques have been sought which relate to photothermographic materials which can be effectively exposed, employing laser imagers and laser image setters, and can form clear black-and-white images exhibiting high resolution.
As described, for example, in Patent Documents 1 and 2, or Non-patent Document 1, known as materials related to the above techniques are heat developable photosensitive materials (hereinafter also simply referred to as photosensitive materials) which incorporate a support having thereon organic silver salts, photosensitive silver halide grains, and reducing agents. Since the above photosensitive materials do not employ any of the solution based processing chemicals, it is possible to provide customers with simpler systems which do not despoil the environment.
Incidentally, in order to minimize degradation of sharpness due to reflection and refraction of incident light during exposure, antihalation (AH) dyes and antiirradiation (AI) dyes have been widely employed in the above photosensitive materials. Listed as characteristics desired for AH and AI dyes are as follows. These dyes sufficiently absorb light of the desired wavelength, do not adversely affect silver halide emulsions, and do not stain photosensitive materials after photographic processing.
However, are known almost no infrared dyes which exhibit the maximum absorption in the near infrared region, especially in the region of 700–850 nm, and which exhibit minimal secondary absorption in the visible region. Listed as a few of such reported examples are squalirium dyes described in Patent Documents 3 and 4. However, in cases in which the described dyes are employed in photosensitive materials, their thermal stability in such photosensitive materials is unsatisfactory, whereby further improvements have been sought.
[Patent Document 1] U.S. Pat. No. 3,152,904
[Patent Document 2] U.S. Pat. No. 3,487,075
[Non-patent Document 1] David A. Morgan, “Dry Silver Photographic Materials”, (Handbook of Imaging Materials, Marcel Dekker, Inc. page 43 to 60, 1991).
[Patent Document 3] Japanese Patent Application Open to Public Inspection (hereinafter it is called as JP-A) No. 58-220143
[Patent Document 4] U.S. Pat. No. 6,482,950